In many areas of chemistry, biochemistry, pharmacology and biology, shaft stirrers are used for the mixing of a reaction medium in a reaction vessel. The stirring is required for example in chemical and/or physical reactions with several phases, when a reaction component is being added, or if components in solid form are present. In heterogeneous reaction media, the stirring has the function of mixing the components thoroughly with each other. In homogeneous reaction media, stirring is often necessary in order to distribute an added substance quickly and thoroughly in the solution, in order to avoid high local concentrations, local overheating, or boiling delays. If a reaction is to be stirred over a longer time period or inside an enclosed reaction vessel, one can use for example a magnetic stirrer or a CPG (core-drawn precision glass) stirrer.
A magnetic stirrer consists of a coated iron element which is inserted into the reaction medium and a drive source which is located outside of the reaction vessel. The known state of the art includes iron elements with diverse shapes, with the shape and length of the iron element being selected to match the dimensions of the reaction vessel and the nature and viscosity of the reaction medium. These stirrers suffer from the drawback that the iron element is difficult to remove from the reaction vessel especially in complex laboratory setups and further that a magnetic stirrer cannot be used for reaction media of intermediate or high viscosity.
A CPG stirrer often consists of a stirrer shaft of glass, where one end of the shaft is configured as, or connected to, a stirrer blade, and the other end of the shaft is connected to an electric motor by way of a coupling. In laboratory applications, one uses for example simply a piece of vacuum hose for the coupling. CPG stirrers can also be used for the mixing of reaction media with higher viscosities. However, because of the electric motor, they characteristically require a large amount of space and can be used effectively only above a certain filling height of the reaction vessel. Furthermore, the reaction vessel as well as the electric motor need to be secured to a suitable post, and stirrer shafts made of glass can be used only in a laboratory environment, because due to the danger of breakage which is inherent in this material they should be continuously monitored.
Further developed versions therefore often have stirrer shafts that are made of other materials such as different metals, ceramics or polymers and are driven by a motor through a suitable coupling.
Shaft stirrers, which in the broadest sense also include the aforementioned CPG stirrers, have the advantage that they can be more easily removed from the reaction medium and that they are also capable of mixing highly viscose reaction media.
The mixing of the reaction medium is influenced on the one hand by the selection of the stirrer blade, the power of the motor, and the selected rate of rotation, but on the other hand also by the orientation of the stirrer blade in the reaction vessel. It has thus been found that if the volume of the reaction medium increases or if the fill level rises, for example if further reagents are added, the position of the stirrer blade should also be readjusted in order to ensure that the rate of mixing remains the same. A position readjustment of the stirrer blade in this context means not only a change of the distance between an inlet port on the reaction vessel and the stirrer blade which is arranged in the reaction vessel, but also a change of the immersion depth of the stirrer shaft into the reaction vessel.
The stirrer is normally fastened to the inlet port by means of a suitable adapter, and both the reaction vessel and the motor are secured on a support stand or a similar device. To provide the capability for adjusting the height of the stirrer blade, it is possible to use for example stirrer shafts of different lengths, and/or extension pieces. This has the disadvantage that, in order to adjust the position of the stirrer blade, it is necessary to either remove the entire stirrer from the reaction vessel, to disassemble and reassemble the stirrer, or to remove at least parts of the setup or of the stirrer.